1. Field of the Invention
The invention relates to a control valve and a fuel injection valve provided with same.
2. Description of the Prior Art
A fuel injection valve is disclosed in DE 197 35 232 in which a damping chamber is provided, which can damp an opening motion of the nozzle needle of the injection valve. The damping chamber is filled with an electrorheological fluid and has an outlet around which two electrodes are disposed. By applying an electric field to the electrorheological fluid in the vicinity of the electrodes, the viscosity of the fluid there can be varied. Correspondingly, the flow resistance changes, which counteracts an escape of the electrorheological fluid from the damping chamber and consequently counteracts an opening of the nozzle needle. In this manner, by suitably producing the electrical field between electrodes as a function of operating parameters of an internal combustion engine in which the injection valve is used, influence can be exerted on the injection behavior of the injection valve.
The object of the invention is comprised in producing a control valve in which different injection cross sections can be produced in a fuel injection valve.
A control valve according to the invention makes it possible to slow or completely inhibit the movement of the displacing element in a virtually arbitrary manner after it travels a particular distance. In this way, the opening behavior of the nozzle needle of a fuel injection valve can be influenced in the desired manner, either directly or indirectly, for example by means of an interposed fluid chamber, without requiring an additional hydraulic control line; only one electrical connection is required for triggering the control valve according to the invention.
According to one embodiment of the invention, the displacing element is a plunger rod which protrudes into the pressure chamber. In this embodiment, when the plunger rod is displaced, only a very slight volume of electrorheological fluid is displaced. For this reason, it is no longer necessary for there to be a buffer chamber with a variable volume which receives the displaced volume; solely the compressibility of the electrorheological fluid makes the corresponding volume displacement possible.
In another embodiment of the invention, the displacing element is provided with a piston which closes the pressure chamber at one end, a buffer chamber is formed on the rear end of the piston, and the pressure chamber is connected to the buffer chamber by means of an overflow conduit. With this embodiment, when there is a small movement of the displacing element, a comparatively large volume of electrorheological fluid is displaced because the piston acts more or less as a booster. Conversely, this means that a relatively small flow resistance and attendant relatively low compressive forces in the electrorheological fluid suffice to produce a high resistance force counter to the movement of the displacing element.
A fuel injection valve according to one embodiment of the invention offers the advantage that a switching between different operating states can be achieved for a low cost, in particular without a separate hydraulic control line. In particular, the electrically switchable control valve makes it possible to brake or stop an opening stroke of the nozzle needle in a virtually arbitrary manner. This is particularly advantageous when the injection valve provides injection orifice selectability so that by selecting the opening stroke, different injection cross sections can be used.